H is a rare one to struggle with because it is a very relaxed sound that does not involve any muscles that are usually involved in speech except for the diaphragm. The sound basically flows out as you breathe out. The only place it can get stuck is if the diaphragm is too tense or if the larynx closes instead of letting the air flow out. Check these two places and if they are relaxed, notice if you might get stuck on the vowel following the H - as someone else on this thread suggested.